TAILFLASH SYNCHRONIZERS FOR ACTION PHOTOGRAPHY

Action photography which combines a blurred image due to a long exposure by
tungsten illumination with an action freezing burst of light from an
electronic flash is no longer an unusual technique.

However, the methods used by photographers to achieve these photographs vary
widely. They range from fortuitous accidents to highly predictable images. The
cost for the equipment used is sometimes negligible but most of the time the
cost in time, materials and equipment is considerable.

Most often the images are built-up "in reverse". That is, the flash is flashed
first and then the action is acted out by the model "backwards". This is so
that the blur will appear to precede the flash, thus indicating the direction
from which the motion is coming. This results in images that look very much
like cartoons of speeding subjects, where the artist adds "speed lines" to
indicate the direction of motion. In cartoons and art these speed lines trail
the subject.

This effect is rather difficult to achieve photographically because shutters
are designed to cause an electronic flash to fire immediately upon (or just
before) reaching their fully open state. Therefore, if you were to attempt
combined tungsten/flash pictures yourself you'd find that when your shutter is
set to a short time exposure or set on B the flash would go off first and the
image due to the tungsten light would trail off in the direction that the
subject is moving. If the subject is moving normally, then the blur in the
picture will appear backwards in relation to artistic convention.

That is why photographers generally deal with the production of these images
under highly controlled studio situations and ask their models to perform a
given motion backwards. Sometimes this is fairly easy to accomplish. With
movements which depend on gravity, however, motions can become rather awkward
when one attempts to perform them backwards.

There are a number of solutions to this problem and often they depend on the
kind of a shutter that your camera is equipped with. The most versatile and
applicable shutter for the successful production of these flash/blur pictures
is the leaf or diaphrag shutter. The larger diameter ones fitted to view
cameras are particularly well suited for this process. If you only have a
focal plane shutter available it can be made to work too but the process is
complicated by the fact that in focal plane shutters the exposure takes place
by the sequential uncovering and covering of the film by the moving curtains
rather than by the simultaneous exposure of the total film gate which is the
case with leaf shutters.

In an attempt to simplify the methods by which a photographer might generate
successful images at a lower cost, I devised two methods for generating a
TAILFLASH or for setting a flash off AFTER the tungsten exposure. One of these
is an electronic method and is designed strictly for use with leaf shutters.
The other is mechanical in nature and can be used with leaf and focal plane
shutters.

Both methods depend on the fact that the trigger circuit of most small
flashguns contains a very small capacitor which is discharged into the trigger
coil at the instant that the camera synchronization contacts close and the
fact that the charging of the trigger capacitor and the main capacitor are for
all intents and purposes isolated from each other.

After a typical handgun is fired, it starts to recharge its main and trigger
capacitors. The trigger capacitor can not recharge, however, until the shutter
sync contacts are opened. This is so because while the contacts are closed the
trigger capacitor is in fact "short circuited" and the charge that would
normally go into it is bled to ground. Since the trigger capacitor is
"insulated" from the main capacitor by high resistances and other protective
circuits, the fact that the shutter contacts, in effect, short circuit the
trigger capacitor does not damage the camera, us or the trigger circuit.
Normally we are not aware of the above fact because we usually do not expect a
flash to fire again while the shutter is still in the open position.

As explained above, a flash is fired when the shutter blades reach their fully
open position causing the sync contacts to close. At the end of the exposure
the blades start to close again and the sync contacts resume their original
open position allowing the trigger capacitor to charge up again. The opening
of the sync contacts generally happens while the shutter blades are still 95%
to 90% still open.

This bit of knowledge along with the fact that most trigger capacitors charge
up to a useable value in a fraction of a second is the basis on which the
following two triggering methods are designed. Both depend on an "inverting"
circuit. That is, one which opens a contact upon another one closing and
closes the contact upon the other one opening.

The use of an inverter circuit is applicable to the solution of this
"tailflash" technique because we would like the flash to go off when the
shutter opens its sync contacts rather than when they close. To accomplish
this you can modify your shutter ( a rather expensive proposition!), buy a
shutter with this feature already buit in ( also expensive ) or improvise a
system as suggested below ( quite inexpensive ).

Anyway, since the shutter sync contacts are normally in an open state the
flash does not fire when it is first plugged into the PC contacts. If you
build the circuit suggested below, however, since it's output contacts are
normally in the closed position the flash will be fired when first connected
to them. After this initial discharge the flash should behave normally and
start to recharge its main capacitor. The trigger capacitor on the other hand
will continnually be bled to ground through the closed contacts of the
inverting circuit or switch.

Then, when the camera's shutter is operated the sync contacts close and the
inverting circuit's contacts open allowing the trigger capacitor to recharge.
This often takes less than 1/4 second. When the exposure is terminated and the
sync contacts start to open again, the contacts of the inverting circuit close
again causing the trigger capacitor to discharge and the flash to fire before
the shutter blades have a chance to move an appreciable distance.

Exposure times of less than 1/4 second may not give the trigger capacitor
enough time to fully recharge and thus should be tested with your particular
unit. Since the closing shutter blades invariably "cut into" the maximum
diaphragm opening of your lens to some extent, smaller than maximum aperture
settings are recommended for predictable exposure control. Most small
flashguns can be operated this way. I have successfully triggered Vivitar and
Sunpack flashes with this synchronizer at exposure times down to 1/15 th
second. If you have trouble with a larger unit then I suggest you slave the
noncooperating flash to one that can be fired reliably.

Here is a later version of the inverting synchronizer scheme built onto a
14 pin IC socket. You may find this circuit easier to build than the one above.
A parts list is included and you can see it in greater detail by calling up the
larger version linked to the thumbnail image.

The above methods and circuits are only suitable for leaf shutters because in focal plane
shutters the camera sync contacts do not open or disconnect until the trailing
curtain has completely covered up the film plane. Thus, the image due to the
flah exposure falls completely on the trailing shutter curtain rather than on
the film. To overcome this problem a simple mechanical inverting switch can be
built based on the use of a microswitch which has a Normally Closed contact.
Most have it, along with contacts identified as Normally Open and Common.

You rig the microswitch up so that an extension from it's feeler arm falls
just above the shutter release button of your camera and you adjust the angle
of the microswitch so that the feeler arm causes the microswitch to "click" as
you start to depress it and to "click" again just before you've let up enough
on the camera's shutter release button to terminate the exposure.

Therefore, as with the electronic version described earlier, when you first
connect your flash to the NC (normally closed) contacts of the microswith your
flash will fire (if it was turned on and fully charged). Then, when you are
ready to start your exposure you depress on the microswitch feeler arm located
directly above the shutter release button. This causes the microswitch to open
it's NC contact allowing the flash trigger capacitor to charge and the
camera's shutter to open as you continue the downward movement of your finger.
When you end the exposure, releasing pressure on the shutter you also allow
the microswitch NC contacts to close again thus setting off the flash before
your finger has risen to point of releasing the trailing curtain of your
camera.

This mechanical version can also be adapted to view camera lenses. It's
advantages are that malfunctions can generally be identified by simply looking
at and listening to the action and that batteries are not required for proper
operation. The electronic version has the advantage of ease of use since it
merely needs to be plugged into the PC connection of the shutter. In either
case, however, it is not so much the device which will yield exciting
pictures but the photographer who learns to use it to its full photographic
potential.